It is known to seal surfaces, particularly those of concrete, by forming thereon a membrane of a bituminous composition or the like which is substantially impermeable to moisture and water vapor. (The term "bituminous composition" as used herein refers to compositions containing asphalt, tar or pitch. The term "concrete" refers to portland cement concrete as well as other similar construction materials). Bituminous compositions can be spray applied in a heated, softened state. A much preferred alternative to these spray applied materials are the waterproofing membranes such as Bituthene.RTM.-brand waterproofing membranes of W. R. Grace & Co. Such membranes typically comprise a primary waterproofing layer of rubberized asphalt adhesive adhered to a carrier sheet of e.g. plastic film. The membranes are sold in roll form with a release sheet of silicone-coated Kraft paper covering the asphalt adhesive layer.
It is known that adhesion of the rubberized asphalt to the concrete surface is greatly facilitated by the application of a primer to the concrete. Primers currently marketed for us in connection with Bituthene-brand membranes are Bituthene primers P-3000 and P-3100, also products of W. R. Grace & Co. These primers are mixtures of rubbers and resins dissolved in organic solvents.
Primers based on aqueous carriers, rather than organic solvents, are desirable. The presence of organic solvents in the workplace is coming under increasing regulatory scrutiny. Unfortunately, water-based latex compositions, as a general rule, do not remain firmly adhered to construction surfaces when immersed in water; they tend to re-emulsify and lose their desired adhesive properties. Another drawback to latex compositions is their tendency to lose stability below a critical temperature of usually about 40.degree. F. Further, the alkaline nature of concrete limits the choice of polymers in the latex to those that will not hydrolyze under these alkaline conditions.
Accordingly, the objects of the invention are to provide a water-based primer composition that is highly compatible with both concrete surfaces as well as the rubberized asphalt adhesives employed in waterproofing membranes.